1. Field of the Invention
The invention relates generally to a circuit configuration and method of manufacturing a transient voltage suppressor (TVS). More particularly, this invention relates to an improved circuit configuration and method of manufacturing a symmetrical bi-directional blocking transient voltage suppressor (TVS) implemented with bipolar transistor base snatch to connect the base to a low potential terminal.
2. Description of the Relevant Art
The conventional technologies for designing and manufacturing a bi-directional blocking transient voltage suppressor (TVS) is still confronted with a technical difficulty that the base of a TVS device is connected to a terminal of floating potential. Typically, the bi-directional blocking TVS is implemented with symmetric NPN/PNP configuration with identical emitter-base and collector-base breakdown voltage. However, such implementation often leads to a floating base that further leads to difficulties of voltage variations over time, i.e., the dV/dt. The voltage variation over time further leads to the leakage current concerns due to the facts that when the base is floating, the voltage change dV/dt causes the equivalent capacitor generating charging and discharging currents that increase the leakage current.
The transient voltage suppressors (TVS) are commonly applied for protecting integrated circuits from damages due to the inadvertent occurrence of an over voltage imposed onto the integrated circuit. An integrated circuit is designed to operate over a normal range of voltages. However, in situations such as electrostatic discharge (ESD), electrical fast transients and lightning, an unexpected and an uncontrollable high voltage may accidentally strike onto the circuit. The TVS devices are required to serve the protection functions to circumvent the damages that are likely to occur to the integrated circuits when such over voltage conditions occur. As increasing number of devices are implemented with the integrated circuits that are vulnerable to over voltage damages, demands for TVS protection are also increased. Exemplary applications of TVS can be found in the USB power and data line protection, Digital video interface, high speed Ethernet, Notebook computers, monitors and flat panel displays.
FIGS. 1A and 1B show a circuit diagram and a current-voltage diagram respectively of a TVS device. An idea TVS is to totally block the current, i.e., zero current, when the input voltage Vin is less than the breakdown voltage VBD for minimizing the leakage current. And, ideally, the TVS has close to zero resistance under the circumstance when the input voltage Vin is greater than the breakdown voltage VBD such that the transient voltage can be effectively clamped. A TVS can be implemented with the PN junction device that has a breakdown voltage to allow current conduction when a transient input voltage exceeds the breakdown voltage to achieve the transient voltage protection. However, the PN junction type of TVS has no minority carriers and has a poor clamping performance as that shown in FIG. 1B. There are alternate TVS implementations with Bipolar NPN/PNP with an Avalanche triggered turning-on of the Bipolar transistor. The base is flooded with minority carriers and the bipolar TVS can achieve better clamping voltage. However, the avalanche current is amplified with the bipolar gain.
With the advancement of electronic technologies, there are increasingly more devices and applications that require bi-directional TVS protections. Devices for audio, ADSL, multiple-mode transceivers, and other electronic devices are required to provide the bi-directional TVS protections as these electronic devices are manufactured with components more vulnerable to transient voltages and operated under more different kinds of conditions that the transient voltage may occur either as positive or negative transient voltages. Currently, the most effective technique to provide the bi-directional TVS is to implement a symmetric NPN/PNP configuration with identical Emitter-Base and Collector-Base breakdown voltage. However, as discussed above, in a conventional bi-directional TVS device as that shown in FIGS. 2A and 2B, to have either symmetrical clamping or unsymmetrical clamping respectively, the base of the TVS in these NPN/PNP circuits are left at a floating potential in order to achieve symmetrical breakdown. The floating base in these implementations causes the dV/dt issues and also the leakage concerns.
Therefore, a need still exists in the fields of circuit design and device manufactures for providing a new and improved circuit configuration and manufacturing method to resolve the above-discussed difficulties. Specifically, a need still exists to provide new and improved TVS circuits that can provide bi-directional symmetrical blocking of transient current to achieve TVS protection by implementing NPN/PNP transistors where the base is always connected to the terminal with a potential such that the above discussed problems and difficulties are resolved.